Lyme disease is caused by infection with the tick transmitted spirochete Borrelia burgdorferi. Arthritis development can occur in individuals not effectively treated during the initial stage of infection. This arthritis is inflammatory in nature, characterized by tendonitis and an influx of polymorphonuclear leukocytes. Studies with a mouse model for Lyme arthritis indicate the pathological developments are associated with invasion of the joint by B. burgdorferi, and the induction of intense inflammation. The bacteria themselves possess outersurface lipoproteins with potent stimulatory activities that could be directly involved in the inflammatory process. The lipoproteins have a fatty acid modification of the amino terminus that is required for the inflammatory activities. Borrelia lipoproteins stimulate B lymphocyte proliferation and cytokine production by a variety of cell types including monocytes/macrophages and endothelial cells. A prototypic lipoprotein, OspA, will be used to characterize the earliest events in cellular activation. The mechanism of cellular targeting by OspA will be studied in human endothelial cells and monocytes. Cellular triggering pathways used by OspA will be compared to those used by bacterial lipopolysaccharide, LPS. CD14 is a molecule found on the surface of monocytes and neutrophils and in serum which facilitates LPS binding and activation of cells. Preliminary studies indicate CD14 is involved in OspA activation of target cells. The ability of anti-CD14 to inhibit OspA induced responses in endothelial cells and monocytes will be determined. The effects of anti-CD14 on early signaling responses such as nuclear translocation of the transcription factor NF-kB and activation of MAP kinases will be measured, as will the later expression of inflammatory cytokines and adhesion molecules. The signaling pathways activated by OspA will be compared with LPS, and the dependence on CD14 for all aspects of cellular activation will be determined. As both pro-inflammatory and anti-inflammatory cytokines are induced by OspA, the effects of these cytokines on OspA induced responses in endothelial cells and monocytes will be determined. Experiments are proposed to allow identification of novel genes whose expression is induced by OspA. Preliminary studies also indicate that the activity of OspA is neutralized by incubation with human or mouse serum. The mechanism by which serum inhibits OspA function will be studied, and effects of OspA structure determined.